Matt Damon slimmed down for “The Talented Mr. Ripley,” plumped up for “The Informant!” and most recently, the actor shaved his head and gained muscle mass for Neill Blomkamp’s (“District 9”) new project“Elysium.”

While the constant gaining-then-shedding of pounds can be physically draining, Matt says it’s all part of bringing characters to life.

“It was just something that Neill kind of saw,” Matt told Access Hollywood’s Scott Mantz at San Diego Comic-Con 2012, of his edgy “Elysium” look. “He saw the guy a certain way, so it just meant that I had to like just literally go to the gym for like 4 hours a day, which was kind of fun in its own way, actually, you know, at my age, to be given an excuse to do that, ‘cause it’s not something you ever really do otherwise!”

The 41-year-old star was happy to be promoting the sci-fi flick at Comic-Con, as he had never been to the famed convention despite his numerous roles in a number of Comic-Con vet Kevin Smith’s films.

“This is my first time here. I don’t think I’ve ever been asked by a studio to come down. I was trying to think, like, [for] some of the earlier Kevin Smith movies, it would have been good,” he said. “But I think Comic-Con has blown up a lot since then too. But we’ve been talking about this since last year — because it was such a big deal for ‘District 9’ — that Neill felt like he didn’t want any footage shown anywhere until Comic-Con.”

“Elysium,” which also stars Jodie Foster, hits theaters on March 1, 2013.